You could use iso extract to adjust it
But if he has less volume at a lower OG is he not more bitter already?
I suppose you could boil some DME and add the right volume/amount to bring the OG and volume back up, but that seems like a PITA.
Sorry...I should have worded this better. I am not looking to adjust the IBU's to get to a certain point. I just want to know what the actual IBU's are now with the changed volume/OG.
I am happy with what it is but I am guessing with coming up short with my OG and volume they are not 49.9 like my program calculated. Just want to know what the new number would be.